1. Field of the Invention
The invention concerns a coil arrangement for a magnetic resonance tomography apparatus.
2. Description of the Prior Art
Magnetic resonance tomography apparatuses are known from DE 10 2005 052 564, for example.
In some applications of nuclear magnetic resonance tomography (MRT), steep and fast gradients would be advantageous; this applies to a particular degree to diffusion-weighted imaging. However, given the gradients used today very significant changes dB/dT or, respectively, dB/dX that can induce electrical currents in the nerve tracts are the result, the gradients are limited by the biological stimulation limit. In principle these limitations can be countered by local gradient systems.
From Parker/Hadley, Magnetic Resonance in Medicine 56:1251-1260 (2006) it is known that local gradients can help to overcome this problem.
An area of magnetic resonance tomography that is increasingly gaining importance is imaging of the female breast, in particular diffusion-weighted imaging. Here strong and fast gradients would be desirable, and in fact primarily in the medio-lateral (X) or anterior-posterior (Y) direction, since here the “decay” of the gradients to the base field strength ensues outside of the body of an examined patient, which is not possible in the Z-direction.
The use of a pot-shaped local gradient coil is known from MRM 39392-401 (1998), Maier et al. However, such a design has specific disadvantages: up, the breast of an examined patient is no longer accessible from the side in order to implemented biopsies, for example. A repositioning of the patient between diagnosis and biopsy is not an optimal solution, however, since the breast thereby shifts and subsequently a lesion can possibly no longer be unambiguously associated. Fixed anatomical landmarks that allow a registration of the images do not exist in the breast in practice.